The way people think of the Solar System has changed many times throughout history.
Before the development of the telescope, these ideas were based on what could be seen with the naked eye. This restricted the details that could be gathered about the Solar System, as asteroids, most of the satellites of other planets, and the most distant planets are not visible to the naked eye.
An Egyptian astronomer called Ptolemy (AD100-168) described one of the earliest ideas for how the Solar System is structured.
Ptolemy’s model and many earlier ideas of the Solar System had the Earth at the centre of it. As observations of the motions of the planets became more detailed, the descriptions of the Solar System had to get very complex in order to keep the Earth at the centre.
Nicolas Copernicus (1473-1543) is generally credited with changing the model of the Solar System to one with the Sun at the centre. Detailed observations with telescopes have given us evidence that this is the correct idea.
Since its discovery in 1930, until 2006, Pluto was counted as the ninth planet in the solar system. In 2006, the International Astronomical Union reclassified it as a ‘dwarf planet’, and our Solar System dropped from having nine planets to eight.